The following is a tabulation of some prior art that presently appears relevant:
U.S. PatentPat. No.Kind CodeIssue DataPatentee4,413,956ANov. 8, 1983Berg4,630,440ADec. 23, 1986Meyerand6,953,328B2Oct. 11, 2005Welch et al7,059,123B2Jun. 13, 2006Welch et al7,188,471B2Mar. 13, 2007Walters7,216,483B2May 15, 2007Takeuchi7,258,532B2Aug. 21, 2007Welch et al
U.S Patent Application PublicationsPublication NumberKind CodePublication DateApplicant20070253841A1Nov. 1, 2007Burns20080231054A1Sep. 25, 2008Estefen20110042955A1Feb. 24, 2011Benson20110074159A1Mar. 31, 2011Stromotich
This application is related to generating energy from water motion on the surface of the ocean, sea, or lake. In particular, this application relates to an advanced method and apparatus realized in an Advanced High Energy Wave Power Module for converting energy from high energy swells and waves to useful forms of mechanical power.
The contemporary directions of generating clean energy without exhaust gases, which pollute the atmosphere, are based mainly on converting solar energy or solar born wind energy directly into useful power. Both directions cannot compete economically with modern technology of generating power based on fossil fuel. The main reason for this is the low density of power generated by solar or wind energy. For example, the maximum density of power generated by solar energy in a hot desert is around 320 watts per square meter. The modern offshore 5 MW wind turbine with diameter of blades up to 120 meters have the density of generated useful power around 440 watt per square meter of air space.
The density of power depends on the density of the medium that accumulates the solar energy. As is known the density of water is almost 1000 times higher than the density of air. Thus, water in the form of swells and waves can accumulate much more solar energy than air in the form of wind.
According to the Techno-Economic Study “The Development of Wave Power”, National Engineering Laboratory, Glasgow, Scotland, 1976 wave power is proportional to the product of the square of wave height and the period of a wave and can be determined with this formula:P=ρg2(H2T)/64σ,whereρ—density of water,g—acceleration due to gravity,H—significant wave height,T—period of wave.
As an example, consider moderate ocean swells, in deep water, a few kilometers off a coastline, with a wave height of 3 meters and a wave period of 8 seconds the power of the wave is 36 kW per meter of wave crest length.
The considerable power of waves attracts and impedes new technologies because the turbulent forces of waves could damage or even destroy the devices that convert the energy of waves into useful power. But solving the issues in transforming the energy of high energy waves into useful power could create a new opportunity for society to produce clean energy with efficiency comparable to that of a modern power plant working on hydrocarbon fuels.
The largest numbers of prior art apparatus which have attempted to harness energy from the moving surface of the ocean have used devices which float and operate on the surface of the ocean to generate mechanical or electrical power. Such devices as Stephen Salter's Duck and the Pelamis Wave Energy Converter are operated with waves of moderate energy. In the case of high energy waves, the operation of the apparatus on the surface of the ocean is restricted because of the possibility of turbulent forces damaging or even destroying the apparatus. Other devices convert the energy of waves into useful power through a point absorber by the float that transfers the energy of the waves to a transforming mechanism, which is submerged to prevent it from being destroyed by turbulent forces.
These mechanisms could be classified into two types, namely electrical generators, and hydraulic or pneumatic converters, particularly hydraulic cylinders that pump water under pressure or pneumatic cameras in which air is compressed by the variable height of passing waves.
The most advanced Power Buoy PB 150 developed by Ocean Power Technology has a point absorber with diameter of the float around 10 meters connected to a submerged vertical mechanism with a height of around 35 meters operated with waves ranging from 1.5 meters to 7 meters in height and generating maximum peak-rated of 150 kW electrical power. The height of mechanism was determined by direct driving from float to generator.
Both U.S. Pat. No. 4,413,956 A to John I. Berg (1983) and U.S. Pat. No. 6,953,328 B2 (2005) to Welch, Jr. have shown the method and apparatus to utilize the energy of waves on the base wave pump apparatus using cylinders with the piston connected directly to the moving float or buoyancy block.
Converting wave energy into useful energy using submersible hydraulic cylinders, pistons or housing cylinders that are driven by the float are practically possible only for waves of moderate height with a moderate energy level because it is impractical to have submerged cylinders with a stroke of 3 or more meters.
Disadvantages of the submersible hydraulic cylinders for wave energy converting are the following:
the long stroke of the movable part of the hydraulic cylinder is equal to the movement up and down of the float, which is moved by the action of waves, such that given a wave of height three meters the movable part of the cylinder should move by three meters; manufacturing of such hydraulic cylinders is a difficult technical challenge and expensive,
losses of energy due the friction of motion in a pair of housing cylinder-piston, which reduces the efficiency of conversion of wave energy into useful energy,
the maintenance of hydraulic cylinders, including replacement of seals in the movable joints operating in salt water, which would require dismantling and disassembly of hydraulic cylinders.
For high energy capacity waves with a height of seven meters and more use of hydraulic cylinders is impractical because the cost of such devices and their reliability cannot compete with modern methods of energy generation.
U.S. Pat. No. 4,630,440 A to Meyerand (1986) has shown a method and apparatus for converting wave energy into useful energy using submersible low-pressure compressible chambers. Variable compression in chambers depends on the hydrostatic pressure of the water column above the compressible chambers during the passage of the waves.
Disadvantages of the low pressure compressible chambers for wave energy converting are the following:
low water pressure in the hydraulic turbine due to low fluctuation of hydrostatic pressure during the passage of the waves. If the height of the wave is three meters an increment of pressure in compressible chambers is only approximately 0.3 bar,
pressure losses due to friction with the transport of water through the piping may be significant comparable to increment of pressure 0.3 bar,
low efficiency of conversion of wave energy into usable energy.